Intra-arterial chemotherapy offers an alternative to systemic (iv) chemotherapy for localized neoplasms. Infusion of chemotherapeutic agents directly into the arterial supply of the neoplasm allows, under the proper circumstances, higher local tissue concentrations without a corresponding increase in systemic toxicity. Intra-arterial infusion rates are commonly in the range of 2 to 5 ml/min through a #5 or #7 French catheter. Results of such infusion have been varied and frequently suggest the possibility of preferential drug perfusion into local sub-regions of target tissue at position distal to the point of infusion. Often, some regions show areas of no drug effect, while other areas exhibit acute toxic responses. The suggestion has been put forward that fluid streaming from the catheter tip during infusion and, thereby, the absence of adequate drug mixing in the efferent blood supply to each arterial branch of the target tissue is one possible cause for the deliterious effects of this treatment modality. The aims of this project were to assess the degree of mixing of solutions infused from catheters into artery-like vessels, and to gain some insight into the fluid-mechanical factors that influence the mixing process. By means of model experiments, we have demonstrated that streaming can occur when infusion rates are too slow for the respective arterial size or arterial flow rates, and that drug solutions streaming at low infusion rates can advance preferentially into specific distal arterial branches. Mixing can be enhanced in numerous ways, e.g. by employing greater infusion rates, or by redesigning the catheter tipes to use "jet" infusion of drug solution transverse to the perfusing blood flow.